An exaggerated unit of measurement used online. When someone claims anything is a certain amount of inches online, those are Internet inches. The actual amount of inches in reality is significantly less.

Toph told Misty he had a 10 inch penis in the chat room. Misty knew that was Internet inches. The real size was much smaller.

Phrase describing a factitious overage given by a man about the size of his penis. In general internet inches adds two or more inches onto the real size of the penis.

Janet: Hey Tommy. Do gay men do the same thing? I'm getting frustrated.
Tommy: About what?
Janet: I started dating this guy I met online and we finally decided to have sex last night. He told me at least 10 times during our dating that he was the "8 incher"...
Tommy: It was six, right? You just gotta love those internet inches.
Janet: Oh so they do it in the gay community too...
Tommy: Dahling....men are men...whether gay or straight..*laughs*